Method of producing cyclopropanes



United States Patent Ofice 3,515,761 Patented June 2, 1970 U.S. Cl.260-666 15 Claims ABSTRACT OF THE DISCLOSURE A method of using apentacyanocobaltate complex to catalyze the formation of cyclopropanesin an aqueous medium is disclosed. 1,3-dihalogenated alkyl hydrocarbonsare reacted in an inert atmosphere at about to 110 C. with thecyanocobaltate and in the presence of an optional stabilizer such as analkali metal halide or hydroxide.

This invention is directed to the production of cycopropanes. Morespecifically, the invention relates to a novel method ofpreparingcyclopropanes from 1,3-d ihalogenated alkyl hydrocarbons incontact with an aqueous solution of a pentacyanocobaltate.

The prior art shows various means of preparing cyclopropanes, but suchmethods are normally expensive, and do not give high yields. Included inthese methods is the use of zinc in various forms in the reaction.Generally the zinc is employed in an alcohol solution with some form ofa halide also present (e.g. atomic iodine, a salt, etc.). Thehydrocarbon cyclized is a 1,3-dihalogenated compound, which in thepresence of zinc is reduced thus forming a cyclopropane and thecorresponding zinc halide. This method has the disadvantage of consumingthe zinc and thus increasing the expense of the reaction. The use ofWerner complexes is also known in the art, but yields in the knownmethods range only to about 80% of theoretical, while the presentinvention has given yields as high as about 90 to 95%.

The method of the present invention involves the reaction in an inertatmosphere of an aqueous cyanocobaltate complex with a1,3-dihalogentated alkyl hydrocarbon thereby causing the cyclopropane toform. The reaction is preferably conducted while in contact with astabilizer for the complex ion. In a specific embodiment, the methodcomprises preparing an aqueous solution by the addition of awater-soluble cobalt salt, e.g. chloride, bromide, or nitrate, and analkali metal cyanide to water in an inert atmosphere and with an excessof cyanide to cobalt, such as a mole ratio of cyanide to cobalt of about5.1 to 7.521, preferably about 5.1 to 73:1, and at a concentration of[Co(CN) ions of about 0.5 to 1.5 molar, preferably 0.1 to 1 molar. Thesolution can be stabilized by the addition of a minor amount, say about0.5 to 5 weight percent, preferably about 1 to 3 weight percent,

based on the total water content, of an hydroxide of halide metal havingan atomic number from 11 to 55. For example the heavier alkali metalhalide can be a chloride or bromide of for instance cesium or rubidium,or the alkali metal hydroxides of sodium, potassium, cesium or rubidium.The stabilizer is not required, but enhances the life of the complexion, and thus is a preferred component. While the above solution isbeing stirred, in the inert atmosphere and at a temperature of fromabout 5 to 110 C., preferably about 20 to 80 C., the 1,3-dihalogenatedalkyl hydrocarbon can be added. As the reaction proceeds the productcyclopropane can be collected as a gas or liquid, depending on itsboiling point.

The 1,3-dihalogenated alkyl hydrocarbon employed in this invention is ofthe general structure:

wherein X is a halogen having an atomic number of from 17 to 53, and Ris hydrogen or an alkyl radical of from 1 to 3 carbon atoms, the totalnumber of carbon atoms in the molecule being up to about 10, preferablyup to about 8.

The present invention will be better illustrated by the followingexamples.

EXAMPLE I An aqueous solution of 0.15 molar potassium pentacyanocobaltwas prepared using 5 gm. cobalt chloride hexahydrate and 7 gm. potassiumcyanide in 140 ml. water and under a nitrogen atmosphere. The solutionwas stabilized by adding 2 gm. of potassium hydroxide, and Was preparedin a 1000 ml. three-neck flask using a 100 ml. addition funnel, a 250ml. gas buret with leveling bulb and a serum cap for the injection ofthe substrate. About 1.0 ml. of 1,3-dibromopropane was injected throughthe serum cap and the immiscible system stirred until about 250 ml. ofgas were generated. The system was maintained at room temperature duringthe reaction. The product gas was analyzed and found to contain:

Percent cyclopropane Propene 19 Propyne Trace Hydrogen Tracel-bromopropane Trace EXAMPLE II The procedure of Example I was repeatedusing a hydrogen atmosphere and employing 7.1 gm. of potassium cyanideand a 0.15 in. potassium pentacyanocobaltate solution, with thefollowing products being obtained.

Percent Cyclopropane 74 Propene 15 Propane 10 EXAMPLE III The procedureof Example I was followed, but 7.1 gm. of potassium cyanide, 2 g. of1,4-dibromobutane, and a reaction temperature of 80 C. were used. Thefollowing are the results of the product gas analysis:

EXAMPLE IV 1,3-diiodobutane was reacted in the manner described inExample III using 1.5 gm. of potassium hydroxide as the stabilizer withthe following products being obtained:

Percent Methylcyclopropane 93 Butene 6 3 EXAMPLE V 1,5-diiodopentane wasreacted in the manner described in Example III with the followingproducts being ob tained:

Percent Cyclopentane Pentene-l 80 N-pentane 10 1,4-pentadiene 7 EXAMPLEVI 1,6-dibromohexane was reacted in the manner described in Example IIIwith the following products being obtained:

- Percent Cyclohexane Hexenes 82 N-hexane 17 EXAMPLE VII2,3-dibrmobutane was reacted in the manner described in Example I withthe following products being obtained:

Z-butene:

Percent Trans 85 Cis 1.1

l-butene Trace It is claimed:

1. A method of producing cyclopropanes from 1,3- dihalogenated alkylhydrocarbons of the general structure:

wherein X is a halogen having an atomic number of from 17 to 53 and R isselected from the group consisting of hydrogen and alkyl hydrocarbons offrom 1 to 3 carbon atoms, the total number of carbon atoms being up toabout 10, comprising reacting said dihalogenated alkyl hydrocarbon in aninert atmosphere and in contact with an aqueous solution of apentacyanocobaltate complex containing an excess of cyanide ions, at atemperature of 2 from about 5 C. to 110 C.

2. The method of claim 1 wherein the cyanide to cobalt mole ratio isabout 5.1 to 7.5: l.

3. The method of claim 2 wherein said pentacyanocobaltate complexconcentration is from about 0.1 to 1 molar.

4. The method of claim 1 wherein there is included in the reactionmixture a minor amount of a stabilizer for the complex, said stabilizerbeing selected from the group consisting of alkali metal halides andalkali metal hydr'oxides, said alkali metal having an atomic numberv 8.The method of claim 7 wherein said temperature 1 is from about 20 to C.

9. The method of claim 8 wherein X is iodine 10. The method of claim 8wherein X is bromine. 11. The method of claim 8 wherein said1,3-dihalogenated alkyl hydrocarbon is 1,3-dibromopropane.

12. The method of claim 8 wherein said 1,3-dihalogenated alkylhydrocarbon is 1,3-diiodobutane.-

13. The method of claim 8 wherein the stabilizer is.

potassium hydroxide.

14. The method of claim 11 wherein the stabilizer is.

potassium hydroxide.

15. The method of claim 12 wherein the stabilizer is potassiumhydroxide.

References Cited UNITED STATES PATENTS 3,450,782 6/1969 Connor 260-6663,074,984 1/1963 Simmons.

2,098,239 11/1937 Hass et al. 260-666 2,102,556 12/ 1937 Hass et a1.260-666 DELBERT E. GANTZ, Primary Examiner V. OKEEFE, Assistant Examiner

